Tuesday, February 21, 2006

These days, one of my junior Scott is wroking hard on the landing skid modification and trial for the T-rex. We need a "higher" landing skid for efficient space to mount some equipments.

Original design is to put T-rex on an big case, then fix this case on one of my Baron's landing skid. This big case is for equipping experiment's sensors or hardwares. Unfortunately, this arrangement does not work. It suffers extreme vibration! This unwanted vibration does not passed even when T-rex takes off. Therefore, Scott searches for another design.

A thinner case is used, and this considerably reduces the vibration. Scott found the aluminium landing gear for small R/C aircrafts yesterday, and he decided to use it to replace the Baron's landing skid.

We test the newest landing skid today afternoon, but T-rex cannot take off smoothly. Maybe the c.g. (center of gravity) is not at proper location, and also T-rex is not adjusted to a good situation. All these, of course, are due to my immature R/C experiences. :p

The yellow sphere is Scott's gimbaled CCD camera set. It's nickname is "紅の豚", and this name means "Red pig".

Thursday, February 16, 2006

I have setup all waht I know, and trim anything I could to do. Of course, there must be something I ignored or did not know.

In fact, Lab's members told me waiting for our pilot Tan Po-hu to test T-rex and adjust it. However, I can not put the helicopter on the table and watch it without imaging flying it!! My fingers told me "Fly~~ Fly it~~", and my mind told me "Warriors are willing to die in the battle rather than die in the peace! So does the T-Rex!! It maybe crash, but crash is far better than be stored to be ruined!!"

So, I and my 2 juniors took the T-rex and some stuff to the grass in front of our institute's building.

At the beginnig, T-rex always tilts its body before lifting off. It was really like a drunk, and we all worried about its safety (and of course ours, too). After several trials, T-rex lifted off the grass! Even I still cannot hover it, but the "control feeling" come up. It's a good start, but the transmitter's battery went into low power. Therefore, we end today's flight test with T-Rex "complete". :p

Wednesday, February 08, 2006

I have to thank God for not let the T-rex take off or there might be a crash. T-rex takes a swashplate design with 3 inputs at 120°. I have no idea that I should select "SR-3" type in the transmitter. Therefore, I cannot figure out why the servos' motion lead to such a strenge movements of the swashplate. For example, why the pitch stick didn't make a "collective" pitch movement? But only tilted one side of it?

Consulting an introduction article, I know that I misunderstood the meaning of CCPM (Cyclic/Collective Pitch Mixing). I always think that CCPM is a particular type of mechanism design which use 3 servos' inputs with 120° arrangement. Hence when I saw the strenge movement of the T-rex's swashplate, I supposed that it is because of the CCPM's design. In fact, it is just because that I didn't choose correct transmitter's parameters (the SR-3 type).

Besides, consulting the Nigel Fraser Ker's tutorial article, I learned about the knowledge of throttle cuve and pitch curve. It has confused me for many years and I never take it seriously due to my own laziness.

Tips:

The linkage about the swashplate could be adjusted by mecahnical or digital way

Make sure the parameters of the transmitter is correct

Good tutorial information could reduce the cost and time considerablely

Monday, February 06, 2006

I repaired the landing skid and replace the plastic CCPM swash plate with a metallic one for T-rex. It looks good!

With the experience yesterday, I have more confidence with today's test. However, I still made some stupid mistakes: Flight without checking all the control surfaces' motion.

The rolling motion is reversed but I was not aware of it. This negligence led to a wrong rolling motion when T-rex was ready to lift up. Again, God blessed this poor helicopter. The main rotor hit the ground, but no visible damage occured.

After correcting the servo's setting of the transmitter, I tried to test T-rex again. Suddenly, one tail blade shoot off!! I am not sure what is the cause. Maybe the tail rotor was damaged in yesterday's "accident", or maybe I didn't screw the tail blade properly.

Actually, T-rex did not really take off. Because I didn't dare to lift it off in our lab's small space, it just slided over the ground.

I will take it to a wider place for next flight test. Of course, it will take off... I hope so...

Saturday, February 04, 2006

After 4 days' efforts, I assemble my first electric RC helicopter. It is not a easy work for me, especially that I have no any experience before.

I follow the instuction manual step by step, and of course do something wrong then correct them. The kit is pretty precise except for the tail boom. The boom has a notch to joint helicopter's body rightly. However, according to its notch, the tail rotor will not be in right angle but somewhat tilt downward. Therefore some modification was done.

In fact, it is not my own helicopter. This small guy is a testbed in my lab. It will carry some equipment to do some experiments. I and my juniors all expect it can take-off and hover smoothly, then we can carry out our experiments during these 2 days.

Unfortunately, because of my lack of related knowledge about electric helicopter, the T-rex breaks one of its landing skid.

When I turn on the transmitter and connect the power on T-rex, then push up throttle slightly... Nothing happened... I think the ESC (Electrical Speed Controller) may be the problem. Because I know nothing about brushless motor and the related ESC, I think that I do something wrong with the ESC. After consulting the manual and do some setting, the main rotor start rotating! Good! but something not normal!! I can't control the RPM!!

The helicopter rotates its balde faster and faster. In that moment I remember that may be the throttle is reversed, and then push up the throttle stick of the transmitter to the end. However, the RPM seems not reduced. I still have no idea that the ESC has a "slow starting fuction" which makes the RPM increase steady and slowly. In other words, this function confused me when I want to reduce the RPM of main rotor.

Finally, I pull down the throttle to the end, and it is really a disaster. The throttle is reversed, so pull down the throttle means increase the RPM!!

Poor T-rex speed up then roll right quickly. It hits one table and only breaks one of its landing skid. It's really a miracle that no more damage on this helicopter.

This is a astonish but good experience to me. I should not mount the motor on the helicopter before I test its running.

GOOD test steps:

Do NOT mount the motor on helicopter. Test the power system alone

Turn on the transmitter

Connect motor, ESC, receiver and battery properly

Try the throttle response

Make sure that the motor can handle via the transmitter, especially the "turn-off"

If you have a electric helicopter and you are also a beginner like me, this test "report" may be useful to you. :-)